4 April 2013
NASA Satellite Measures The Effects Of Greenland Block That Stopped Spring
Posted by Dan Satterfield
NASA image from the MODIS sensor on the Aqua satellite showing temperature anomalies between 14-20 March 2013. The warmth over Greenland caused by the blocking high is clearly visible along with the resulting chill over eastern areas of North America, and much of Western Europe. Click image for a LARGE version.
I mentioned the North Atlantic Oscillation in a recent blog post. The Arctic Oscillation is closely related to the NAO and many meteorologists often use the two interchangeably. The AO and NAO have been in a deeply negative phase for several weeks and this has brought unseasonably cold weather to Eastern North America and Western Europe. So cold, that a Ohio prosecutor indicted a Pennsylvania rat (AKA Punxsutawney Phil) for fraud, after a prediction that spring was (and I quote here) “Just around the corner!”
The good news is that this pattern is rapidly breaking down. Not good news if you are hoping for a suntan in Greenland, but for those in the Northeast U.S. and Western Europe, spring is about to be sprung!
Here is what NASA had to say about the image and there is a great link to a table produced by Capital Climate showing that this event was one of the strongest on record:
Image ctsy. NASA showing how strongly negative the Arctic Oscillation has been for around 8 weeks.
While a high-pressure weather system brought warmer than normal temperatures to Greenland and northern Canada in March 2013, much of North America, Europe, and Asia shivered through weeks of unseasonably cool temperatures. The contrasting temperatures are no coincidence: the same unusual pressure pattern in the upper atmosphere caused both events.
Cornell Univ. image. Good piece here about how the extremes in the index may be related to the decreasing Arctic sea ice. http://livasperiklis.com/2012/06/11/cornell-chronicle-arctic-ice-melt-sets-stage-for-cold-weather/
Atmospheric pressure patterns are constantly in flux, as air masses of differing temperatures and densities move around the skies. One key measure of pressure that meteorologists track closely is known as the Arctic Oscillation (AO) index, the difference in relative pressure between the Arctic and the mid-latitudes. Changes in the AO have can major impacts on weather patterns around the world.
When the AO index is in its “positive” phase, air pressure over the Arctic is low, pressure over the mid-latitudes is high, and prevailing winds confine extremely cold air to the Arctic. But when the AO is in its ”negative“ phase, the pressure gradient weakens. The pressure over the Arctic is not as low and pressure at mid-latitudes is not as high. In this negative phase, the AO enables Arctic air to flow to the south and warm air to move north.
In late March, the AO dropped as low as -5.6. (See this chart published by the Washington Post’s Capital Weather Gang to see how this compares with other periods when AO values reached record-low levels).
The temperature anomaly map above, based on data from the Moderate Resolution Imaging Spectroradiometer(MODIS) on NASA’s Aqua satellite, shows how this affected temperatures in the Northern Hemisphere. The map displays land surface temperature anomalies between March 14–20, 2013, compared to the same dates from 2005 to 2012. Areas with above-average temperatures appear in red and orange, and areas with below-average temperatures appear in shades of blue. Much of Europe, Russia, and the eastern United States saw unusually cool temperatures, while Greenland and Nunavut Territory were surprisingly warm for the time of year.
Many parts of the Northern Hemisphere saw near record-breaking cool temperatures as the value of the AO fell. The United Kingdom experienced its 4th coldest March since 1962. In late-March, two-thirds of weather stations in the Czech Republic broke records. Germany saw its coldest March since 1883. And Moscow had its coldest March since the 1950s.
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References
- Climate Central (2013, March 19) From Heat Wave to Snowstorms, March Goes to Extremes. Accessed April 1, 2013.
- Der Spiegel Online International (2013, March 28) White Easter: Germany Faces Coldest March Since 1883. Accessed April 2, 2013.
- Earthsky (2013, March 22). Officially spring, but feels like winter for many in U.S. Accessed April 1, 2013.
- Met Office (2013, March 28) Coldest March for the UK since 1962. Accessed April 2, 2013.
- NOAA Arctic Oscillation (AO). Accessed April 1, 2013.
- Prague Daily Monitor (2013, March 28) Cold weather breaking records. Accessed April 2, 2013.
- Washington Post (2013, March 24) Record blocking patterns fueling extreme weather: detailed look at why it’s so cold. Accessed April 1, 2013.
Dan’s Note:
Model guidance out to 15 days is all indicating that the AO and NAO are going to switch to a strong positive phase. That means it will get a lot warmer!
From NOAA CPC.
Dan Satterfield has worked as an on air meteorologist for 32 years in Oklahoma, Florida and Alabama. Forecasting weather is Dan's job, but all of Earth Science is his passion. This journal is where Dan writes about things he has too little time for on air. Dan blogs about peer-reviewed Earth science for Junior High level audiences and up.
Hi Dan,
Thank you for the blog.
Do the Mets in the USA have a reason for the AO being so negative this March. After all, the AO is only a record of pressure difference from a mean average value. I think that we have seen a unique number of variables come together to create this effect. These being prolonged downwelling stratospheric negative mean zonal wind anomalies which were enhanced by a burst of wavenumber 1 activity at the start of March. On top of these we have had a negative QBO flushing out polewards from the lower stratosphere to enhance the negative anomalies since the start of the year. We have had an increased continental snow gain last October which has combined with a warmer Arctic to ‘spread out’ the polar field leaving the jet stream weaker, more meridional and very southerly positioned. Finally, have the years of reduced solar activity somehow coming into play?
How long will we have to wait before we see another March so below average?
Regards
Chionomaniac
based in the UK
Although a negative NAO and AO are indicative of colder weather at mid-latitudes they are only indexes and cannot explain the causes of the fundamental weather pattern. So when you say: “Changes in the AO can have major impacts on weather patterns around the world.” It would make more sense to put it the other way around and say: “Changes in the weather patterns around the world can have a major impact on AO.” …as you say, it is just a “measure of pressure (differences)”.
Both are true I think 😉
ds
I don’t think it was the UK’s 4th coldest March since 1962. It WAS the COLDEST March since 1962 as it says in the link you provided. March 2013 turned out to be the 2nd coldest March in the UK series after the final month data had been colated.